Antisurge valve for hydraulic wood grinders



Jan. 16, 1951 P. R. SANDWELL 2,533,383

ANTISURGE VALVE FOR HYDRAULIC woon GRINDER-S Filed Sept. 23, 1948 3 Sheets-Sheet 3 INVEN TOR. 6290/1/4 Patented Jan. 16, 1951 UNITED STATES PATENT OFFICE ANTISURGE VALVE FOR HYDRAULIC VVOOD GRINDERS Percy Ritchie Sandwell, Vancouver, British Columbia, Canada Application September 23, 1948, Serial No. 50,830

, 5 Claims (0!. 1'21 46.5)

Groundwood paper mills produce wood pujp solely by the mechanical action of large grinders which are frequently hydraulically operated and hydraulically controlled These grinders may be operated individually or in multiple banks oftwo, three or more grinders to each bank. Each of the grinders so arranged generally includes a turbine-driven grindstone and one or more pulpwoodcharging pockets, each of which includes a reciprocable ram or presser foot for forcing pulpwhich the governor cannot immediately compenwood from a supply hopper into contact with the surface of the associated grindstone.

Each bank of rinders or even an individual grinder receives a supply of water under substantial pressure from a main water supply;

through a suitably designed governing device which may be, for example, of thetype disclosed in U. S. Letters Patent 1,450,380, granted April 3, 1923, to A. F. Meyer. The primary function of such governing devices is to maintain a continuous flow f operating water to the grinders at such pressures and rates of flow as to maintain substantially uniform grinding load on the grindstones at substantially constant speeds of rotation of the grindstones.

When the presser foot of a grinder pocket has been retracted or backed off to permit recharging the pocket with a new supply of p-ulpwood the demand for high pressure water from the governor for that particular grinder pocket ceases and the governor must adjust itself to the continuing water demand of all other pockets which remain in feed or grinding operation. This phase of the grinding operations seems to have been satisfactorily handled by known typesof governors.

However, when such a grinder pocket has been recharged with pulpwood and grinding operations are to be restarted with respect to such pocket, forward or feeding movement of the presser foot is initiated by appropriate movement of the maneuvering control valve of the pocket to admit offset by an increase in available water due to' control action by the governor. When the presser foot pushes the pulpwood into initial pressure contact with the grindstone a temporary but substantial increase in loading pr ssureis caused for.

sate, in other words, known governors for pulp grinders operate in such a manner that temporary surge loading on the grindstone cannot be avoided whenever the presser foot is advanced to first bring a new charge of wood into grinding contact with the grindstone.

it is therefore an object of this invention to provide novel means usable in conjunction with a hydraulically operated and controlled pulpwood grinder for eliminating shock loading effects on the grindstones whenevera new charge of wood is just brought into grinding contact therewith by a presser foot.

Another object of this invention is to provide means of the character stated which consists of a control valve assembly which is interposed between the governor and a grinder pocket and which is adapted normally to permit free passage of high pressure water from the governor during the grinding phase and to cut off the flow of high pressure water during the latter part of the feed stroke of the presser foot in the grinder pocket while simultaneously permitting the flow of low pressure water from a separate source to complete the feed stroke of the presser foot.

Another object of this invention is to provide a device of the character described which comprises a three-chambered valve casing having two inlet chambers and an outlet chamber with pressure-controlled disc valves operationally positioned within the chambers to eiTect change of flow from high pressure water to low pressure water and back to high pressure water.

Another object of this invention is to provide a device of the character stated which is effective to permit the initial flow of high pressure water to the cylinder of a grinder pocket for initiating the feed stroke of a presser foot and which will automatically cut off the flow of high pressure water as soon as the feed stroke of the grinder presser foot has commenced, simultaneously permitting a flow of low pressure water through another chamber of the valve for completing the feed stroke of the presser foot, there being means provided for bleeding high pressure water from the high pressure side of the valve to the low pressure outlet of the valve during and upon completion of the feed stroke of the presser foot so that the pressures between high and low pressure sides may become equalized, and high pressure water may again be admitted to the grinder cylinder for the grinding phase of operations by automatic actuation of the valve discs within the casing. v

cylinder of a grinder pocket together with its associated control valves and the. intermediate surge load eliminating valve with which this'invention is particularly concerned, the valves all being shown in the positions'for starting a-feed stroke of a grinder pocket presser foot;

Fig. 2 is an enlarged longitudinal section of the surge .load eliminating valve constructed in accordance with this invention" and shows its component parts in the position assumed during the midde portion of the feed stroke of a grinder pocket presser foot;

Fig. 3 is a view'similar to Fig. 2 but'shows the component parts of the valve assembly in the positions taken after the completion of the feed stroke of a presser foot when high pressure water is'again being admitted to the cylinder; and

Fig. 4 is a view similar to Fig. l but shows the parts in the'position during backing off of the grinder pocket presser foot with the piston being shown as it approaches the end of its retractive or backing ofif stroke.

By reference to the drawings in detail it will beseen that this invention is applied to a hydraulic grinder with only those parts of the grinder which are pertinent to this invention being shown in detail. By reference to Figs. 1 and 4 of the drawings it will be-seen that a cylindergenerally indicated at 5 having a cylinder head 6, a feed stroke water passage 1 "and abacking off'water passage g'is provided with a piston 9*to which is rigidly afii'xed a piston rod or ram Ill. The other end of the piston rod 19 passes through a'glandin the opposite end of the cylinder 5-"(not sh'own) andcarries the usual presser foot (not shown) for forcing pulpwood into contact with the grindstone. Since the general assembly of hydraulic 'pulpwood' grinders is well known to th'ose skilled in the art no attempt h'as been made herein to illustrate thecomplete grind- Immediately below the cylinder 5 is a piston control valve assembly-generally indicated at H which includes a casing l2 having an inlet port indicated by dotted lines at l3 for admitting feed stroke andgrindin'g pressure water and a second inlet port indicated by dotted lines at it for admitting backing 'off water. This control valve assembly may be considered as typical of'this art in'rthatthe passage of waterfrom either of the inletports'lt and It to respectively correspondin'goutlet passages l5 and it occurs through eitherpair of'annular chambersll, l? or l8; IS in accordance with the position of a dual valve piston generally indicated at 19 which is reciprocally mounted within a suitably apertured bushing sleeve 26. The dual piston I 9 carries a'piston' rod 2i which extends outwardly beyond the casing [2 through a-spacing spider 22 "into an actuating cylinder 23'. A double faced valve actuating piston 24 is mounted on the outer end of the rod'2l within the cylinder'23. Inlet ports of the cylinder 23 and serve to admit low pressure water to either end of the cylinder for valve operating purposes from a supply of low pressure water which passes through a master control or maneuvering valve generally indicated at 21.

The maneuvering valve 21 is also a piston valve and includes an outer casing 28, an internal reciprocable piston 29, an inlet port indicated by dotted lines at 3!] and a pair of outlet passages 3| and 32. The piston is carried by a piston rod SE -which .passesthrough a gland 36 and is operably connected to a control handle 35 through appropriate-connecting links.

Thesurge load eliminating valve which is constructed in accordance with the instant inventi'onispreferablyplaced below the control valve assembly H as indicated in Figs. 1 and 4 of the drawings. This valve comprises a casing 36 having a large internal chamber divided into a lefthand portion 31, a right-hand portion 38 and a centrally disposed annular discharge portion 39. An inlet port Allis in open communication with the chamber portion 3'! and a similar inlet port l is in open communication with the chamber portion 38. A centrally disposed disc 42 having airaperture 43 forms one wall i the annular chamber 39 and a similar disc M, having an aperture 45 forms another wall of the annular chamber 39. One wall portion of the chamber section 31 is closed by a removable plug 45 having an inwardly projecting stud 4'! formed integral therewith. The stud portion 3'! is provided with a counter bore &8 and a bushing 49. Avalv'e stem 5? which has a reduced end portion 5! slidably carried by the bushing 43 is provided at its other end with a similarly reduced end portion 52 slidably carried in a bushing 53 mounted in an inwardly projecting stud portion 54 of a removable plug 55 closing off one wall portion of 'the chamber portion 38.

Within the chamber 3'! the valve stem 5% car ries ashouldered collar 56 which is adapted to receiveone end of a compression spring the other end of which is seated adjacent the base of the inwardly projecting stud t? of the end plug 45. Thus thecompression spring El will always tend to force a movement of the valve stem 53 to the right as viewed in all of the figures of the drawings. A valve disc 58 is rigidly affixed to the valve stem 59 within the chamber porton 38 and is adapted to beseated on the adjacent face of the disc 44 and thus control flow of fiuid through the aperture 45. A similar valve disc 591s freely mounted on the central portion of thevalve stem within the space between the discs 42 and 44 and is adapted to seat on the adjacent face of the disc 42 and thus control passage of fluid through the aperture 33. A compression spring 66 surrounds the valve stem and extends between the rigidly afiixed valve disc 58 and the freely movable valve disc and thus tends to constantly urge the valve disc 53 towards seating contact with the disc 42.

The upper wall portion of the chamber 38 is provided with a vertically disposed bore E! which extends into open communication with a horizontally disposed bore 62 which in turn opens into communication with the discharge area of the annular chamberportion 39. The outer end of the'borefi2 is closed by a removable plug 63. A needle valve .64 .is threadably engaged in the upper portion'of the. casing and is disposed in alignment with the vertically arranged bore 5! 25 and 26 are located adjacent the respective ends 15 so that the pointed needle end thereof may become seated at the juncture between the bores BI and 62 or may be slightly spaced therefrom in order to permit a restricted flow of fluid from the chamber portion38 into the discharge seotion 39. The needle valve (it may be locked into any desired position as through the medium of a lock nut 65. 7

It may have been observed from the foregoing description that the hydraulic system as herein disclosed is designed for operation by both low pressure and high pressure water. The maneuvering valve 2'! receives low pressure water from a source of supply and transmits it to the actuating cylinder 23 of the piston control valve assembly H. This portion of the low pressure watr, incidentally, also actuates the charging door (not shown) of the wood supply hopper which is located adjacent the grinder pocket through mechanisms which are contained in a cylinder generally indicated at 65 which is disposed in parallelism with the main presser foot actuating cylinder 5. In this system low pressure water is also always used for the backing off movement of the presser foot to permit a recharging of the grinder pocket with fresh wood. In so far as the feed stroke of the presser foot is concerned that motion is initiated by high pressure water and as soon as feeding motion of the piston 9 has commenced a pressure drop within the cylinder will cause the high pressure water to be cut off and low pressure water to be admitted until the feeding stroke of the presser foot has been completed. At this time the low pressure water is cut off from the feeding end of. the cylinder 5 and high pressure water again admitted in order to maintain full grinding pressure. The flow diagram for the piping to effect these general operations is indicated on the drawings by dotted lines. Low pressure water is received from a suitable source of supply through the medium of a pipe 6'! which may connect directly with the inlet port 40 of the surge load control valve assembly. A pipe 68 may branch oii' from the pipe 67 and lead up to the intake port of the maneuvering valve 2'5. Another pipe 5% may branch off from the pipe 63 and lead to the inlet port It of the piston control valve assembly H. From the maneuvering valve 2? the low pressure water is admitted to the port 25 of the piston valve actuating cylinder 25% through a pipe i6 and in a similar manner water is carried from the maneuvering valve to the port 25 through a pipe N. High pressure water from the governor is connected to the system through a pipe '52 which may be directly connected to the inlet port ti of the surge load control valve assembly. Pipe 73 connects the discharge port 39 of the surge load control valve assembly with inlet port it of the piston valve assembly Ii. It may be of interest to note the typical water pressures which may be employed in hydraulic grinder systems of this nature, namely, a lowpressure water on the order of i0 lbs. per square inch and high pressure water on the order of lbs. per square inch. With a pressure differential of this nature it has been found that the surge load control valve operates quite satisfactorily and that through the use of low pressure water of this indicated pressure to effect at least the latter portion of the feed stroke or" the presser foot no abnormal surge loading is met with on the grindstone.

Hydraulic grindel ystems of this type describe herein may be considered to operate through three phases in a complete g n y The firstphase is the charging or feeding phase in which the grinder pocket presser foot pushes a new charge of pulpwood into contact with the grindstone. The second phase may be termed the grinding phase and during this period full grinding pressure is applied by the presser foot. The third phase is the backing oil phase during which the presser foot is retracted so that a fresh supply of pulpwood may be introduced into the grinder pocket. In Fig. 1 of the drawing the parts are all shown in the position to initiate the first phase of the cyclic operation outlined above.

With the maneuvering valve 2? being in the position indicated in Fig. l the low pressure water flows through its outlet port 3| down through the pipe Hi and into the cylinder 23 through the inlet port 26', thus causing the piston 24 to be moved to the extreme right of its limit of movement and correspondingly effecting the positioning or the dual piston valve i9 to permit a flow of water into the feed stroke water passage 1 of the main cylinder 5. The elements of the surge load control valve assembly at this instant are in the positions indicated in Fig. l and high pressure water will flow from the pipe indicated at E2 through the inlet port ii, the right-hand chamber 38, and since the valve disc 58 is raised from its seated position relative to the seating disc it the water will flow through the aperture 35 into the discharge passage 33- No high pressure water can flow through the aperture 43- since the pressure dii ferential between the chamber portions 3'! and 39 is such that the high pressure water flowing through the chamber portion 39 will effectively keep the valve disc be seated. This high pressure water will flow from the control valve assembly through the pipe 13 into the inlet 53 of the valve assembly ii, and consequently it is this high pressure water which initially starts a motion of the piston 9 and its associated presser foot. As soon as this forward feeding movement of the piston 9 starts under the influence of high pressure water a pressure drop is caused in the line between the inlet port ll of the surge load control valve and the piston. This pressure drop will eficct a pressure differential between the chamber portions 38 and 39 of the surge load control valve assembly sufficient to cause the valve disc 53 to become seated on its seating disc M against the action of the spring 51, thus closing 01? the aperture 35 and preventing the flow of any more high pressure water to the main cylinder 5. Since the flow of high pressure water from the chamber 38 is prevented by the closing of the valve disc 58 low pressure water in the chamber 32- becomes effective to raise the valve disc 59 oil its seat against the action of the spring 6 to permit the flow of low pressure water into the discharge chamber passage 38 and thus into the main cylinder 5 through the control valve assembly ii. In this manner further feed motion of the presser foot is effected solely by low pressure water. Fig. 2 of the drawings indicates the positions of the various elements of the surge load control valve assembly during this portion of the feed stroce.

' When the piston S of the main cylinderand its associated presser foot have moved forward a sufficient distance to push the fresh charge of pulpwood into contact with the grindstone initial grindstone pressure is el'lected only by low pressure water since that is the only water available to act on the head of the piston 9 at this particular instant of time; The low pressure=water does not develop; sufiicient grinding pressure to appreciably movethe presser foot forward and consequently the flow of water through the system into the cylinder substantially ceases. At this time high pressure water from the chamber 38 which has been bleeding through from the chamber 38 to the chamber 39 .via' the bores 6| and 62 under the restrictive control of the needle valve 64 becomes effective through the bleeding action to approximately equalize the pressures between the chamber 38 and-the chamber 39. As the pressures approach equality the spring 51 becomes effective touunseat the valve disc 58 and again permit the flow of high pressure water through the aperture into: the discharge chamber 39. This flow of high pressure water, of course, will also effect a seating of the disc valve 59 and prevent .the flowof high pressure water into the low pressure water chamber portion 37. Fig. 3 of the drawings illustrates the position of the several elements of the surge load control valve at this point in the operations. With .the flow of high pressure water again taking place full grinding pressure is restored to the presser foot and normalgrinding continues.

When it becomes necessary to recharge the grinder pocket with fresh pulpwood the maneuvering valve 2! is shifted to the position indicated in Fig. 4 ofthe drawings so that low'pressure water-will flow through the outlet passage 32 and the pipe ll into the cylinder 23 through its inlet port 25. Thus the actuating piston 24 will be forced to move to the extreme-leftof its limited movement as viewed in Fig. 4, and the dual valve piston It will partake of a corresponding movement to cut off the flow of water into the passage l of the main cylinder assembly 5 and initiate the flow of low pressure backing off water through the passage -8. The low pressure backing off water is received through the inlet port i4 of the valve assembly II and of course flows into the passage 8 and from there into the cylinder 5 and acts on the left-hand face of the piston 9 to impart the backing 01f movement to it and'its associated presser foot. As the piston is thus being'retracted the water which is at thehead of the piston and in the passage 1 is discharged through an exhaust duct or passage 74 in the control valve casing l2 and a d1scharge pipe ind-icated by dotted lines at E5. In a like manner the spent water from the maneuvering valve 21 is discharged through an exhaust passage 16 and a discharge pipe indicated by dotted lines at 11. During the backing off movement of the presser foot as outlined above the several elements of the surge load control valve are in the positions indicated in Fig. 4 which are identical to the positions illustrated in Fig. 3. No movement of the valve disc elements of this surge load control assembly can takeplace since the dual piston is of the-control valvell effectively closes oil passage of any water from its inlet port 13 to any other portion of the system. Obviously, unless water could flow through the port l3 and the control valve assembly II no water can flow through the surge load control valve assembly, and the parts must remain in a static condition.

Thusit will be seen that the invention-disclosed herein provides novel means particularly useful in hydraulically controlled pulpwood grinders in which certain operative steps are efiected through the use oflow pressure water and zotheroperative steps are effected through highpressure Water; and'in which high pressure water is employed to initiate the feeding stroke of a presser foot and as soon as the feed stroke has been initiated will cause an automatic shift from high pressure water to low pressure water for the purpose of completing the feed stroke; and which becomes thereafter effective to again admit high pressure water for the grinding phase.

It is, of course, to be understood that various details of arrangements and proportions of parts may be modified within the scope of the appended claims.

I claim:

1. A surge-load preventing valve for hydraulic grinders comprising a casing having a lateral chamber extending into open communication with a centrally disposed annular chamber, a first inlet port formed in said casing adjacent one end of said lateral chamber and adapted to be connected to a source of high pressure water, a second inlet port formed in said casing adjacent the other end of said lateral chamber and adapted to be connected to a source of low pressure water, a discharge port formed in said casing and extending into open communication with said an-v nular chamber, a pair of spaced annular valve seats rigidly afiixed to said casing within the cen-- tral portion of said lateral chamber and effective to divide said chamber into a high pressure portion, a low pressure portion and a centrally located discharge portion, a valve stem reciprocably mounted within said lateral chamber and extending through said valve seats, a biasing spring connected with said valve stem and effective to constantly urge it toward the high pressure portion of' said chamber, a valve disc rigidly aifixed to said stem within said high pressure chamber portion and adapted to be seated on one of said annular valve seats, a second valve disc freely mounted on said valve stem and positioned intermediate said valve seats and being adapted to be seated on the other of said valve seats, and a biasing spring interposed between said first and second valve discs and effective to constantly urge said second valve disc toward seating engagement with its associated valve seat, said casing being provided with a bieeder duct extending between said high pressure and annular chamber portions whereby to effect substantial equalization of pressures therebetween after such times as said first valve disc has become seated on its associated valve seat and said second valve disc has become unseated to permit passage of low pressure water to said discharge port.

2. A surge-load preventing valve for hydraulic grinders comprising a casing having a lateral chamber extending into open communication with a centrally disposed annular chamber, a first inlet port formed in said casing adjacent one end of said lateral chamber and adapted to be connected to a source of high pressure water, a second inlet port formed in said casing adjacent the other end of said lateral chamber and adapted to be connected to a source of low pressure water, a discharge port formed in said casing and extending into open communication with said annular chamber, a pair of spaced annular valve seats rigidly affixed to said casing within the central portion of said lateral chamber and effective to divide said chamber into a high pressure portion, a low pressure portion and a centrally located discharge portion, a valve stem reciprocably mounted within said lateral chamber-and extending through said valve seats, a biasing second valve discs and effective to constantly urge said second valve disc toward seating engagement with its associated valve seat, said casing being provided with a bleeder duct extending between said high pressure and annular chamber portions whereby to efiect substantial equalization of pressures therebetween after such times as said first valve disc has become seated on its associated valve seat and said second valve disc has become unseated to permit passage of low pressure water to said discharge port, and means for regulating the flow of fluid passing through said bleeder duct,

3. A surge-load preventing valve for hydraulic grinders comprising a casing having a lateral chamber extending into open communication with a centrally disposed annular chamber, a first inlet port formed in said casing adjacent one end of said lateral chamber and adapted to be connected to a source of high pressure water, a second inlet port formed in said casing adjacent the other end of said lateral chamber and adapted to be connected to a source of low pressure water, a discharge port formed in said casing and extending into open communication with said annular chamber, a pair of spaced annular valve seats rigidly aifixed to said casing within the central portion of said lateral chamber and effective to divide said chamber into a high pressure portion, a low pressure portion and a centrally located discharge portion, a valve stem reciprocably mounted within said lateral chamber and extending through said valve seats, a biasing spring connected with said valve stem and effective to constantly urge it toward the high pressure portion of said chamber, a valve disc rigidly affixed to' said stem within said high pressure chamber portion and adapted to be seated on one of said annular valve seats, a second valve disc freely mounted on said valve stem and positioned intermediate said valve seats and being adapted to be seated on the other of said valve seats, a biasing spring interposed between said first and second valve discs and effective to constantly urge said second valve disc toward seating engagement with its associated valve seat, said casing being provided with a bleeder duct extending between said high pressure and annular chamber portions whereby to effect substantial equalization of pressures therebetween after such times as said first valve disc has become seated on its associated valve seat and said second valve disc has become unseated to permit passage of low pressure water to said discharge port, and a needle valve threadably engaged in said casing for regulating the flow of fluid passing through said bleeder duct.

4. In a hydraulic grinder wherein is provided a cylinder, a presser foot piston slidably carried within said cylinder, a high pressure water connection communicating with one end of said cylinder for normally imparting a feed stroke to said presser ioot piston in one direction, a low pressure water connection communicating with the other end of said cylinder for normally cf fecting a retractive stroke to said presser foot piston in the opposite direction, and a master control valve connected with said low pressure water line for controlling the direction of movement of said presser foot piston; the combination of a surge-load preventing valve including a casing having an inlet port connected with a high pressure Water line, a second inlet port con nected with said low pressure water line, a discharge port connected to the high pressure end of said cylinder, a pair of spaced annular valve seats secured within said casing and dividing the interior thereof into a high pressure chamber, a low pressure chamber and a discharge chamber, a first valve disc positioned within said discharge chamber and operably associated with one of said valve seats for controlling passage of fluid from said low pressure chamber to said discharge chamber, a second valve disc positioned within said high pressure chamber and operably associated with the other of said valve seats for controlling passage of fluid from said high pressure chamber to said discharge chamber, spring means for biasing said second valve disc away from seating contact with its associated valve 'seat, and spring means extending between said valve discs for biasing said first valve disc toward seating contact with its associated valve seat, said valve discs being operable by fluid pressure and being automatically eifective in accordance with variations of pressure within said casing, first to permit high pressure water to fiow into said cylinder when said master control valve has been positioned to initiate a ieed stroke of said presser foot piston, secondly to close off the fiow of high pressure water to said cylinder at such time as a pressure drop occurs in the said high pressure line during the feed stroke of said presser foot piston and simultaneously to admit low pressure water to continue said feed stroke of said presser foot piston, and finally upon completion of the feed stroke of said presser foot piston to again admit high pressure water to said cylinder so that full mechanical pressure may be applied by said presser foot piston, said valve casing being provided with a bleeder passage extending between said high pressure and discharge chambers.

5. A surge-load preventing valve for hydraulic grinders comprising a casing having a lateral chamber extending into open communication with a centrally disposed annular chamber, a first inlet port formed in said casing adjacent one end of said lateral chamber and adapted to be connected to a source of high pressure water, a second inlet port formed in said casing adjacent the other end of said lateral chamber and adapted to be connected to a source of low pressure water, a discharge port formed in said casing and extending into open communication with said annular chamber, a pair of spaced annular valve seats afiixed to said casing within the central portion of said lateral chamber and dividing the interior thereof into a high pressure chamber, a low pressure chamber and a discharge chamber; a first valve disc positioned within said discharge chamber and operably associated with one of said valve seats for controlling passage of fluid from said low pressure chamber to said discharge chamber, a second valve disc positioned within said high pressure chamber and operably associated with the other of said valve seats for controlling passage of fluid from said high pressure chamber to said discharge chamber, spring means for biasing said 7 '11 second valvedisc awayfrom seating contact with its associated valve seat, and spring means extending between said valve discs for'biasingsaid first valve disc toward seating contact with its associated valve seat, saidvalve discs being operable by fluid pressure and being automatically efiective in accordance with variations of pressure within said casing,'first to permit a flow of highpressure water through said high pressure and discharge chambers while preventing any flow of low pressure water through said 10W pressure chamber aridlbeing automatically operable upon the occurrence of a pressure drop occurring through said discharge port to efiect the shutting off of high pressure water and the admission of low pressure water, and'finally being automati cally operable upon substantial equalization of pressures between said discharge and high pressure chambers to again permit the 'fiow of high pressure water and the shutting off of low pressurewater, said casing being provided with a bleeder passage extending, between. said high J2 pressure and ,dischargechambers whereby'the pressures therebetween may become gradually equalized during such (times as h ighpressure water is 'direct1y.cut off from said -discharge chamber and low pressure .water is admitted thereto.

PERCY RITCHIE SANDWELL.

REFERENCES CITED Thei following referencesare .of record in..1;ne file. of this patent:

UNITED -S'I ATESI PATENTS Number Name Date 718,474 "Kasson Jan; 13, 1903 652,710 Dotterweich "Dec. 13, 1927 2,189;221 Paine Feb. 3.6, i 1940 FOREIGN PATENTS Number Country Date 561,681 Great Britain -May 31, 1944 

